Radiation treatment or radiotherapy involves the treatment of a disease with radiation, typically by selective irradiation with x-rays or other ionizing radiation and/or by ingestion or surgical implantation of radioisotopes. During radiation treatment, for example, high-energy x-rays or electron beams are generated, e.g., by a linear accelerator (LINAC) and directed towards a target (e.g. a tumor). The goal of the treatment is to destroy the cancerous cells within the target without causing undue side effects that may result from harming surrounding healthy tissue and vital organs during treatment.
To treat regions within the body of the subject, however, the radiation must typically penetrate healthy tissue in order to irradiate the internal treatment volume and destroy pathological cells therein. In conventional radiation therapy, large volumes of healthy tissue can thus be exposed to harmful doses of radiation, resulting in prolonged recovery periods for the patient. Radiotherapy treatment plans are often constructed to achieve the desired on-site exposure whilst keeping the exposure of healthy cells to a minimum.
Many methods work by directing radiation at a tumor from a number of directions, either simultaneously from multiple sources or multiple exposures from a single source. The intensity of radiation emanating from each source is therefore less than would be required to destroy cells, but where the radiation beams from the multiple sources converge, the intensity of radiation is sufficient to deliver a therapeutic dose.
The point of intersection of the multiple radiation beams is herein referred to as the “target point”. The radiation field surrounding a target point is herein referred to as the “target volume”, the size of which can be varied by varying the size of the intersecting beams.
Radiation treatment typically takes place over one or a course of several sessions during which a delivered radiation dose is broken into a plurality of portal fields. For each field, a LINAC gantry is rotated to different angular positions, spreading out the dose delivered to healthy tissue. At the same time, the beam remains pointed towards the target anatomy, which may be placed in the isocenter of the beam by positioning the patient.
Such radiation therapy is rationally delivered with the radiation source revolving around the patient superior/inferior axis. The source trajectory is referred to as coplanar geometry. Coplanar source trajectories are simpler to plan and deliver.
Although adding beams from non-coplanar trajectories can improve the dosimetry and reduce normal organ doses from radiotherapy, such treatment methods are not easily achievable due to the difficulties in plan optimization, collision avoidance and the creation of an efficient beam path so that a non-coplanar plan can be delivered within the time allowed by clinical work flow.